The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.

When using the Index Replication feature, Apache Solr nodes can pull index files from a master/leader node using an HTTP API which accepts a file name. However, Solr before 5.5.4 and 6.x before 6.4.1 did not validate the file name, hence it was possible to craft a special request involving path traversal, leaving any file readable to the Solr server process exposed. Solr servers protected and restricted by firewall rules and/or authentication would not be at risk since only trusted clients and users would gain direct HTTP access.

Apache Solr uses a PKI based mechanism to secure inter-node communication when security is enabled. It is possible to create a specially crafted node name that does not exist as part of the cluster and point it to a malicious node. This can trick the nodes in cluster to believe that the malicious node is a member of the cluster. So, if Solr users have enabled BasicAuth authentication mechanism using the BasicAuthPlugin or if the user has implemented a custom Authentication plugin, which does not implement either "HttpClientInterceptorPlugin" or "HttpClientBuilderPlugin", his/her servers are vulnerable to this attack. Users who only use SSL without basic authentication or those who use Kerberos are not affected.